1. Field of the Invention
This invention relates to the surgical fixation of prostheses in fractured, diseased and necrotic bones. More specifically, it concerns the use of sterile, biocompatible, non-biodegradable, high molecular weight, atoxic, inelastic, thermoplastic polymers which melt at ranges of from about 45.degree. C. and are rigid solids below about 42.degree. C. for fixation of prostheses to bone in surgical procedures of the hip joint, in osteoarthritis, rheumatoid arthritis, traumatic arthritis, avascular necrosis, non-union of fractures of neck and femur, sickle cell anemia, revision of previous arthroplasty procedures, fractures of the neck of the femur in the elderly suitable for prosthetic replacement, and unstable fractures in individuals with metastatic malignancies.
2. Description of the Prior Art
The fixation of endoprostheses in calcified tissue plays an important role in orthopedic surgery. Ideally, products used for this purpose should have handling characteristics and physical and chemical properties which are peculiarly suitable for this purpose. For example, the material should not adhere to the surgeon's glove when it is ready to be used and it should be easy to apply in the presence of moisture and set soon after without dimensional changes or the generation of excess heat.
Most importantly, a material for use in fixing prostheses into bone should be biocompatible, nonabsorbable, rigid at body temperatures, sterilizable, have a low level of histotoxicity and lack carcinogenicity.
A number of polymeric compositions have been used by surgeons in recent years for fixing prostheses into bone, the most widely used being polymethyl methacrylate. However, many difficulties are associated with this material, both with respect to the surgeon and the patient. Since the monomer is highly volatile and flammable, the operating room must be provided with adequate air circulation. In practice, the monomer must be admixed with methyl methacrylate-styrene copolymer to give it the desired cementitious characteristics. During the mixing, caution must be exercised to prevent excessive exposure to the vapors of the monomer which may produce irritation of the respiratory tract, eyes and possibly liver.
Another disadvantage of methyl methacrylate is its property as a powerful lipid solvent. It should not be allowed to come into direct contact with sensitive tissues or be absorbed by the body since the monomer is suspected of being toxic. Furthermore, the uncontrolled heat rise resulting from the polymerization reaction may cause necrosis of the bone.
Other materials recommended for use in bone fixation include various derivatives of alpha-cyanoacrylate such as methyl alpha-cyanoacrylate, monomeric alkoxyalkyl 2-cyanoacrylate, alpha-cyanoacrylate esters and compositions containing these substances together with other additives including polymers. Like the polymethyl methacrylates, the use of these materials requires the introduction of monomers into the bone area, and the monomers polymerize in situ to form a permanent, polymeric composition.
This invention provides a method for fixing prosthetic devices into bone tissue which is simple, convenient, atoxic to surgeon and patient, and reversible. It eliminates the present need for conducting polymerization reactions in situ, avoids the preparation of the compositions requiring volatile monomers or solvents, and affords the opportunity to remove the prosthesis at any time by the simple application of heat within a temperature range which is not dangerous to the patient.